Entire cities, like Douma, pictured here, have been ravaged by the conflict in Syria

With a vast array of competing factions involved in the war it can be difficult to wrap your head around what's really going on on the ground.

But now the war is the subject of a new two-part BBC2 documentary, Syria: the World's War, which aims to trace the conflict back to its roots and chart how it has evolved.

The roots of the crisis

Canadian journalist Lyse Doucet, explains on the doc that the current war begun in 2011, following the "Arab Spring", a wave of protests in the Middle-East and North Africa where ordinary civilians rose up against authoritarian governments.

The unrest in Syria started in March that year, growing out of discontent with President Bashar al-Assad, who rose to power with a rigged election in 2000 and has cracked down on the freedoms of Syrians ever since.

The Syrian Civil War has pulled disparate alliances of states together

A rebellion emerges

The anti-Assad rebels were united by their hatred of the president, but they were otherwise disparate, with different rebel factions clashing with each other as they pushed for their own kind of revolution.

As tensions rose, and Assad's army tried harder to suppress protesters, members of the movement started taking up arms to defend themselves.

After six months of protests, a full-scale civil war broke out.

Government tanks rolled into Homs, firing at ordinary Syrians and destroying buildings.

Meanwhile, Western leaders, like then US President Obama, started calling for Assad to step aside.

As bombs fell and cities were ruined, refugees were driven out of Syria

For three years, the US had held back from airstrikes against Assad – but they couldn’t sit by and do nothing while IS, plotting deadly terror attacks in the West, grew stronger.

So in September 2014, they sent their first fighter jets to the country.

Meanwhile, it looked as if the regime would lose control of Aleppo – many of the hard-line Islamist fighters joined the rebels there, and the rebels took the city of Idlib.

This is when Putin came in to lend a hand to his ally, and by October 2015, the first Russian planes appeared over Aleppo.

The UK was also pressurised into fighting - but against IS, rather that the regime.

With a Commons vote under David Cameron, we vowed to launch targeted airstrikes against ISIS held territory and became one of the many nations involved in Syria’s tangled war.

In total, the doc claims 75 countries have been affected by the crisis in some way: either by funding or supporting a group on either side, by taking part in strikes or through involvement with the displaced refugees.

The rebel grip on Aleppo was eventually weakened by government strikes

The deliberate targeting of hospitals is a war crime – but the Syrian Government said Al-Qaeda terrorists were using it as a base in order to justify their attack. The medical staff at the hospital said this was untrue.

By now, the Syrian army and its allies could sense victory.

The rebels, fatigued and out-gunned, were losing ground - and on 22 December 2016 the four-year Battle of Aleppo was over, won by the regime.